1.5. SIGNAL GENERATOR
BASIC PRINCIPLE OF OSCILLATORS
1. What is the primary function of an oscillator in electronic circuits?
A. Voltage amplification
B. Frequency multiplication
C. Signal modulation
D. Signal generation
Answer: D. Signal generation
Explanation:
The primary function of an oscillator is to generate a continuous waveform or signal, typically a sine wave, square wave, or other periodic waveforms.
2. What is the Barkhausen criterion for oscillation in an oscillator circuit?
A. Positive feedback equal to unity and phase shift of 360 degrees
B. Negative feedback equal to unity and phase shift of 0 degrees
C. Positive feedback greater than unity and phase shift of 0 degrees
D. Negative feedback greater than unity and phase shift of 360 degrees
Answer: C. Positive feedback greater than unity and phase shift of 0 degrees
Explanation:
According to the Barkhausen criterion, for sustained oscillations, the loop gain (product of gain and phase shift) around the feedback loop must be greater than unity, and the total phase shift around the loop must be 0 degrees or a multiple of 360 degrees.
3. Which type of oscillator circuit uses an LC (inductor-capacitor) tank circuit for frequency determination?
A. Colpitts oscillator
B. Wien bridge oscillator
C. Crystal oscillator
D. Hartley oscillator
Answer: D. Hartley oscillator
Explanation:
In a Hartley oscillator, the frequency of oscillation is determined by an LC tank circuit, typically consisting of an inductor and capacitor in parallel.
4. What is the role of the Wien bridge network in a Wien bridge oscillator?
A. Voltage amplification
B. Frequency stabilization
C. Phase shifting
D. Negative feedback
Answer: B. Frequency stabilization
Explanation:
The Wien bridge network in a Wien bridge oscillator is used for frequency stabilization, allowing the oscillator to produce a stable frequency output.
5. Which type of oscillator circuit uses a quartz crystal for frequency control?
A. RC oscillator
B. Crystal oscillator
C. Colpitts oscillator
D. Hartley oscillator
Answer: B. Crystal oscillator
Explanation:
Crystal oscillators use a quartz crystal for frequency control, providing high stability and accuracy in frequency generation.
6. In an LC tank circuit of an oscillator, what role does the inductor play?
A. Frequency stabilization
B. Phase shifting
C. Energy storage
D. Voltage amplification
Answer: C. Energy storage
Explanation:
The inductor in an LC tank circuit of an oscillator plays the role of storing energy, creating resonance and determining the frequency of oscillation.
7. What is the purpose of the feedback network in an oscillator circuit?
A. To provide voltage amplification
B. To introduce phase shift
C. To generate harmonic distortion
D. To sustain oscillations
Answer: D. To sustain oscillations
Explanation:
The feedback network in an oscillator circuit is designed to provide positive feedback and sustain oscillations, meeting the Barkhausen criterion.
8. What is the significance of the term "quenching" in oscillator circuits?
A. It refers to frequency multiplication.
B. It indicates a decrease in oscillation amplitude.
C. It signifies the introduction of negative feedback.
D. It denotes the process of starting oscillations.
Answer: B. It indicates a decrease in oscillation amplitude.
Explanation:
In oscillator circuits, quenching refers to the intentional reduction of the oscillation amplitude, often used in relaxation oscillators.
9. What is the purpose of the buffer amplifier in a crystal oscillator circuit?
A. Voltage amplification
B. Frequency stabilization
C. Phase shifting
D. Signal generation
Answer: A. Voltage amplification
Explanation:
The buffer amplifier in a crystal oscillator circuit is used for voltage amplification to compensate for the crystal's inherent low output impedance.
10. Which type of oscillator circuit is known for its low phase noise and high frequency stability, commonly used in precision applications?
A. Colpitts oscillator
B. Wien bridge oscillator
C. Relaxation oscillator
D. Crystal oscillator
Answer: D. Crystal oscillator
Explanation:
Crystal oscillators are known for their low phase noise and high frequency stability, making them suitable for precision applications such as in frequency synthesizers and communication systems.
RC, LC AND CRYSTAL OSCILLATOR CIRCUIT
1. In an RC oscillator, what is the primary purpose of the resistor (R) and capacitor (C) components in the feedback network?
A. To provide voltage amplification
B. To introduce phase shift
C. To store energy and create resonance
D. To control the frequency of oscillation
Answer: D. To control the frequency of oscillation
Explanation:
In an RC oscillator, the resistor (R) and capacitor (C) components in the feedback network are used to control the frequency of oscillation.
2. What type of waveform does an LC oscillator typically generate?
A. Sine wave
B. Square wave
C. Triangle wave
D. Sawtooth wave
Answer: A. Sine wave
Explanation:
LC oscillators, such as the Hartley and Colpitts oscillators, typically generate sine wave outputs.
3. What is the function of the crystal in a crystal oscillator circuit?
A. To provide voltage amplification
B. To introduce phase shift
C. To store energy and create resonance
D. To provide frequency stability
Answer: D. To provide frequency stability
Explanation:
The crystal in a crystal oscillator circuit is used to provide high frequency stability, making it suitable for precision applications.
4. What is the key advantage of using LC tank circuits in oscillator circuits?
A. Voltage amplification
B. High frequency stability
C. Low power consumption
D. Low harmonic distortion
Answer: B. High frequency stability
Explanation:
LC tank circuits offer high frequency stability in oscillator circuits, making them suitable for applications requiring precise frequency control.
5. In an RC phase shift oscillator, how many RC networks are typically used to achieve the required phase shift for oscillation?
A. One
B. Two
C. Three
D. Four
Answer: C. Three
Explanation:
An RC phase shift oscillator typically uses three RC networks to achieve the required 180 degrees phase shift for positive feedback and oscillation.
6. What is the primary function of the inductor in an LC oscillator circuit?
A. To provide voltage amplification
B. To introduce phase shift
C. To store energy and create resonance
D. To control the frequency of oscillation
Answer: C. To store energy and create resonance
Explanation:
The inductor in an LC oscillator circuit plays a key role in storing energy and creating resonance, influencing the frequency of oscillation.
7. In a Colpitts oscillator, what components determine the frequency of oscillation?
A. Resistors and capacitors
B. Capacitors and inductor
C. Resistors and inductor
D. Inductor and crystal
Answer: B. Capacitors and inductor
Explanation:
In a Colpitts oscillator, the frequency of oscillation is primarily determined by the values of capacitors and the inductor in the tank circuit.
8. What is the primary advantage of using a crystal oscillator over other types of oscillators?
A. Higher voltage gain
B. Higher frequency stability
C. Lower power consumption
D. Lower harmonic distortion
Answer: B. Higher frequency stability
Explanation:
Crystal oscillators offer higher frequency stability compared to other types of oscillators, making them ideal for applications requiring precise and stable frequency outputs.
9. In an LC tank circuit, what happens to the frequency of oscillation if the value of the inductor increases?
A. The frequency decreases.
B. The frequency increases.
C. The frequency remains constant.
D. The frequency becomes unpredictable.
Answer: A. The frequency decreases.
Explanation:
In an LC tank circuit, the frequency of oscillation is inversely proportional to the square root of the inductance, so an increase in inductance results in a decrease in frequency.
10. What is the primary function of the amplifier in an oscillator circuit?
A. To provide voltage amplification
B. To introduce phase shift
C. To control the frequency of oscillation
D. To generate the initial signal
Answer: A. To provide voltage amplification
Explanation:
The amplifier in an oscillator circuit provides voltage amplification to compensate for the energy losses in the feedback network and sustain oscillations.
WAVEFORM GENERATOR
1. What is the primary function of a waveform generator in electronic circuits?
A. Voltage amplification
B. Frequency multiplication
C. Signal modulation
D. Signal generation
Answer: D. Signal generation
Explanation:
The primary function of a waveform generator is to generate various types of waveforms, such as sine waves, square waves, and triangular waves, for use in electronic circuits.
2. Which type of waveform generator is commonly used for generating stable and precise sine wave outputs?
A. Pulse generator
B. Function generator
C. Relaxation oscillator
D. Crystal oscillator
Answer: B. Function generator
Explanation:
Function generators are commonly used for generating stable and precise sine wave outputs along with other types of waveforms.
3. What is the key advantage of using a function generator over a simple oscillator circuit?
A. Higher frequency stability
B. Higher voltage gain
C. Greater waveform variety
D. Lower harmonic distortion
Answer: C. Greater waveform variety
Explanation:
Function generators offer the advantage of producing a variety of waveforms, including sine, square, triangular, and more, providing versatility in circuit testing and experimentation.
4. In a pulse generator, what parameter is typically adjustable to control the width of the generated pulses?
A. Frequency
B. Amplitude
C. Duty cycle
D. Rise time
Answer: C. Duty cycle
Explanation:
In a pulse generator, the duty cycle parameter is adjustable to control the width of the generated pulses, representing the ratio of pulse width to the pulse period.
5. Which type of waveform generator is known for its square wave outputs and is widely used in digital applications?
A. Function generator
B. Pulse generator
C. Relaxation oscillator
D. Crystal oscillator
Answer: C. Relaxation oscillator
Explanation:
Relaxation oscillators are known for generating square wave outputs and are commonly used in digital applications and clock circuits.
6. What is the primary application of a sweep generator in electronic testing?
A. Voltage amplification
B. Frequency modulation
C. Voltage regulation
D. Frequency sweeping
Answer: D. Frequency sweeping
Explanation:
Sweep generators are used for frequency sweeping, allowing testing and analysis across a range of frequencies in electronic circuits.
7. What parameter is adjusted to control the frequency of the waveform generated by a voltage-controlled oscillator (VCO)?
A. Amplitude
B. Frequency modulation
C. Duty cycle
D. Voltage input
Answer: D. Voltage input
Explanation:
The frequency of a voltage-controlled oscillator (VCO) is controlled by adjusting the voltage input, providing a convenient method for frequency modulation.
8. Which waveform generator is commonly used for generating rectangular waveforms with variable duty cycles?
A. Function generator
B. Pulse generator
C. Sweep generator
D. Square wave generator
Answer: A. Function generator
Explanation:
Function generators are versatile and can be used to generate rectangular waveforms with variable duty cycles, making them useful in various applications.
9. In a frequency synthesizer, what is the primary function of the phase-locked loop (PLL)?
A. To provide voltage amplification
B. To introduce phase shift
C. To control the frequency of oscillation
D. To synchronize frequencies
Answer: D. To synchronize frequencies
Explanation:
The phase-locked loop (PLL) in a frequency synthesizer is used to synchronize frequencies and generate stable output frequencies.
10. What is the primary advantage of using a crystal-controlled oscillator in a waveform generator?
A. High frequency stability
B. Greater waveform variety
C. Variable duty cycle
D. Low harmonic distortion
Answer: A. High frequency stability
Explanation:
Crystal-controlled oscillators offer high frequency stability, making them suitable for applications where precise and stable frequency outputs are required, such as in waveform generators.